1. Field of the Invention
The present invention relates to systems, methods, and apparatuses for wireless communication to communicate with a plurality of terminals or stations using Space Division Multiple Access (SDMA) with one and the same frequency at one and the same point of time, and in particular, to systems, methods, and apparatuses for wireless communication in which resources of space and time are efficiently allocated in consideration of Quality of Service (QoS).
2. Description of the Related Art
Attention has been drawn to antenna and signal processing techniques capable of tremendously improving the utilization efficiency and the transmission rate of wireless frequencies. One of such techniques is called “Adaptive Array Antenna (AAA)” to adjust, by use of weighting coefficients or weights, amplitude and phases of signals communicated respectively via a plurality of antennas. This improves the signal-to-noise ratio and increases the system communication capacity or channel capacity. There is known a technique “Multiple Input Multiple Output (MIMO)” which increases the data transmission rate using the AAA technique. According to the MIMO system, the channel capacity can be increased by installing, between a transmitter and a receiver, channels the number of which is equal to at most the number of antennas. Additionally, these techniques, when viewed from another perspective, can be categorized into (1) Space Division Multiple Access (SDMA) to transmit signals to two or more stations and (2) Space Division Multiplexing (SDM) to transmit signals to one and the same station. In the SDMA technique, the amplitude and phases of signals communicated respectively via a plurality of antennas are adjusted using weights to transmit mutually different data sequences to a plurality of stations with one and the same frequency at one and the same point of time by use of the spatial orthogonality of the signals on the transmission paths. On the other hand, according to the SDM technique, the amplitude and phases of signals communicated respectively via a plurality of antennas are adjusted using weights to transmit mutually different data sequences to one and the same station with one and the same frequency at one and the same point of time by use of the spatial orthogonality of the signals on the transmission paths. Also, there is known a technique “MIMO-SDMA” implemented as a combination of the SDMA and MIMO techniques. In the MIMO-SDMA technique, the SDMA technique is employed for different terminals and the SDM technique is utilized for the one and the same terminal. The SDMA technique is described, for example, in an article, T. Ohgane, “A Study on a channel allocation scheme with an adaptive array in SDMA” IEEE 47th VTC, Vol. 2, 1997, pp. 725-729. The SDM technique is described, for example, in an article, G. J. Foschini, “Layered space-time architecture for wireless communication in fading environment when using multi-element antennas”, Bell Labs Tech. J. Autumn 1996, pp. 41-59. The MIMO-SDMA technique is described, for example, in an article, Andre Bourdoux, Nadia Khaled, “Joint Tx-Rx Optimisation for MIMO-SDMA Based on a Null-space Constraint”, IEEE2002. pp. 171-172.
A need exists for a technique which meets the requirement for various application services in addition to the requirement for a higher transmission rate in the wireless communication. These applications have requirements of communication quality such as transmission bands and allowable transmission delay associated with communications thereof. Various schemes have already been discussed to guarantee such requirements for the application services.